Two piece mold used in manufacture of PDC drill bits and method of using same

ABSTRACT

A graphite core mold having its own cavity is pressed into a cavity of a graphite shell mold. The core cavity is filled with tungsten carbide, mixed with a nickel alloy, heated and then cooled to thereby provide a carbide matrix body. After milling the carbide matrix body to thereby provide a carbide bit body, the intact shell mold is removed and then used again.

BACKGROUND OF INVENTION

This invention relates generally to the manufacture of fixed cutter drill bits used to drill oil and gas wells.

Various types of drill bits have been developed and found useful in different drilling environments. Bits typically used for drilling boreholes in the oil and gas industry include roller cone bits and fixed cutter bits. Cutting structures on bits vary depending on the type of bit and the type of formation being cut. Roller cone cutting structures typically include milled steel teeth, tungsten carbide inserts, or diamond enhanced inserts. Cutting structures for fixed cutter bits typically include polycrystalline diamond compacts, commonly referred to as “PDC” cutters. The selection of a bit type and cutting structure for a given drilling application depends on many factors including the formation type to be drilled, rig equipment capabilities, and the time and cost associated with drilling.

It is common in the art of manufacturing PDC, fixed cutter drill bits, to manufacture the carbide matrix body of the drill bit in a graphite mold. Such a mold known in the prior art is typically made with a single mold manufactured from graphite.

Fixed cutter drill bits, also referred to as fixed head bits or drag bits, are generally more expensive than mill tooth roller cone drill bits and are considered to offer less aggressive cutting structures than roller cone drill bits. However, in several applications, fixed cutter bits can be used to drill longer well segments in a single run and can be rebuilt and reused multiple times to provide an overall economic benefit that outweighs the higher cost. Fixed cutter bits which include PDC cutters are typically referred to as PDC bits.

FIG. 1 of the drawings illustrates a conventional single piece graphite mold which is known in the prior art for manufacturing the carbide matrix body for a PDC drill bit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial, isometric view of a graphite mold known in the prior art used for manufacturing a carbide matrix body for PDC drill bits;

FIGS. 2A, 2B and 2C respectively illustrate an exploded view of the two piece mold in accordance with the present invention;

FIG. 3A illustrates another view of the elements illustrated in FIGS. 2A, 2B and 2C, as assembled, after the drill bit has been at least partially milled in accordance with invention;

FIG. 3B is a schematic view, partially in cross section, illustrating the assembled two piece mold and the gauge ring which is used as a funnel, illustrated in FIG. 2C, resting on top of the two piece mold illustrated in FIGS. 2A and 2B;

FIG. 4A is an elevated, schematic view, in cross section, illustrating the mold core illustrated in FIG. 2 mounted within the mold shell illustrated in FIG. 2A and having the gauge ring illustrated in FIG. 2 sitting on top of the mold part shown in FIG. 2B;

FIG. 4B is a top plan, schematic view of the embodiment illustrated in FIG. 4A, but without its top portion illustrated;

FIG. 5 is a side view, in cross section of the mold shell illustrated in FIG. 2A in accordance with the invention;

FIG. 6 is a side view, in cross section, illustrating the mold core illustrated in FIG. 2B, which in operation resides within the mold shell illustrated in FIG. 5;

FIG. 7 is a pictorial, isometric view of the assembled two piece mold illustrated in FIGS. 2A and 2B, and having a drill bit residing within the interior of the mold core in FIG. 2B in accordance with the invention; and

FIG. 8 illustrates the equipment used in milling the drill bit within the mold core illustrated in FIG. 2B while resting on a fixture to support the mold core illustrated in FIG. 2B.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings in more detail, FIG. 1 is a pictorial, isometric view of the one piece mold which is commonly used in the PDC drill bit industry to manufacture PDC bits. The mold 10 has a lower portion 12 and an upper ring 14 which contains a cavity which is used as the mold for manufacturing the PDC bit body. In the process of using the prior art mold illustrated in FIG. 1, the mold is first partially filled with a tungsten carbide powder to which is then applied a metal alloy, such as a nickel alloy. Upon heating, the nickel alloy will mix with the molten tungsten carbide, which upon cooling results in a carbide matrix which forms the bit body in the prior art. A conventional milling process such as is illustrated in FIG. 8 having milling device 16 is then used to mill out the various components of the matrix body to result in a finished PDC matrix body.

In using the single piece mold of the prior art illustrated in FIG. 1, as soon as the process has been finished as illustrated in FIG. 1, the mold 10 is removed from the molded graphite 18, typically by breaking the mold 10 with a hammer, a crowbar or the like. This results in a lot of wasted material because the mold 10 cannot be reused because of its broken condition.

Referring now to FIGS. 2A, 2B and 2C, there is illustrated a mold shell 30 and a mold core 32 which is illustrated in FIG. 2B. The mold core 32 is sized to closely fit within the cavity 34 illustrated in FIG. 2A which allows the mold core 32 to be easily removed from the shell 30 after the molding process has been completed. The mold shell 30 is not broken and can be reused several times in the molding process. As illustrated in FIG. 2B, the milling process has been used to at least partially complete the milling of the matrix body to result in a matrix drill bit body. Gauge ring 36 which sits on top of the mold shell 30, surrounds the cavity in the mold core 32, all is illustrated in FIG. 4A.

The funnel 38 through which the nickel alloy and the tungsten carbide powder is filled, allows the tungsten carbide powder and the nickel alloy to go into the cavity within the mold core 32 as illustrated in FIG. 2B. Sitting atop the funnel 38 is a top end piece 42. The end cap 42 can be threaded onto the top of the funnel 38 or can merely sit on top of the funnel as desired. In FIG. 4A, the drill bit parts, are illustrated schematically, such as the nozzles 44 and the other components such as the cutter pockets 46 which will eventually house the PDC cutters once all the molding process has been completed. All of these parts of the conventional PDC bit are well known in the art and need no further description herein.

FIG. 4B illustrates a top plan view of the mold shell, mold core and gauge ring, as well as carbide matrix which has been milled to accept the various components of the finished drill bit in accordance with the invention.

FIG. 7 is a pictorial, isometric view of the two piece mold according to the invention, is much like the embodiment of FIG. 3A, but having the milling process further completed for forming the various components of the PDC drill bit. Assuming that the milling process is completed, the core 32 is easily removed from the mold shell 30, without any need to break the mold shell 30, all as contemplated by the present invention. The matrix body for the drill bit can then be removed from the mold core, with breaking of the mold core as may be necessary. It allows a mold shell to be used several times without a need to break the shell as done in the prior art single piece molds. The use of the two piece mold enables the manufacture of several sized PDC bit bodies from a single size mold shell which cannot be done in the prior art because the one piece mold is broken with a single use and does not allow the manufacture of different sized drill bit bodies to be made from a one piece mold, or even a repetition of the process for the same sized bits using the same shell. 

1. A mold for forming a carbide matrix PDC bit body, comprising: a cylindrical shell having a closed end, an open end and a cavity commencing with the open end of said shell; a cylindrical core having a closed end, an open end, and a cavity commencing with the open end of said core, said core having an outside diameter sized to closely fit within the inside diameter of the cavity within said shell, wherein the cavity within the core can be filled with a mixture of tungsten carbide powder and particles of a metallic alloy, which when heated and then cooled and then milled, form a carbide matrix PDC bit body.
 2. The mold according to claim 1, wherein said core comprises graphite.
 3. The mold according to claim 2, where said shell comprises graphite.
 4. The mold according to claim 1, wherein the closed end of said core and the closed end of said shell are pressed against each other.
 5. The mold according to claim 1, wherein said metallic alloy comprises nickel.
 6. A method for molding a carbide matrix body for a PDC drill bit, comprising the steps of: pressing a graphite core into a graphite shell; pouring tungsten carbide powder and particles of a metallic alloy into a cavity in said core; melting the mixture of the powder and the particles within the cavity in the core; cooling the molten mixture to thereby provide a carbide matrix body; removing the intact shell from around the core; milling the carbide matrix body with the desired features of a PDC drill bit; and removing the core from the carbide matrix body.
 7. The method according to claim 6, including the repetition of the steps according to claim 6, using the same graphite shell in the repeated process.
 8. The method according to claim 6, wherein the metallic alloy comprises nickel. 